Generally, a washing machine is an apparatus to wash laundry using electricity. Washing machines are classified into a drum washing machine and a vertical-axis washing machine. The drum washing machine is provided with a rotary tub horizontally arranged, such that laundry is washed by having the laundry lifted along an inner circumferential surface of a rotary tub and fallen when the rotary tub rotates about a horizontal axis thereof in forward and backward directions. The vertical-axis washing machine is provided with a rotary tub including a pulsator vertically arranged, such that laundry is washed using a water stream generated by the pulsator when the rotary tub rotates about a vertical axis thereof in forward and backward directions.
Generally, the drum washing machine includes a cabinet, a tub placed within the cabinet to store wash water therein, and a drum rotatably installed in the tub to receive laundry to be washed therein. An opening may be provided in the cabinet, and the opening may be opened or closed by a door.
The drum rotates to agitate laundry along with wash water on the condition that the laundry, detergent, and the wash water are put into the drum, such that dirt or stains are removed from the laundry. The laundry is put into the tub through the opening provided in the cabinet, and detergent and wash water are supplied by a detergent supply device.
If a washing process of the drum washing machine starts operation, the door of the drum washing machine remains locked. In order to allow laundry to be easily put into or taken out of the drum during the washing process, the door of the drum washing machine may include an auxiliary door to be freely opened or closed at any time desired by a user.
If the auxiliary door is opened during the washing process, detergent bubbles generated in the drum may leak outside through the opening opened or closed by the auxiliary door.